The present invention relates to a layer forming material for forming copper wiring on a substrate, and also to a copper wiring forming method.
Conventionally, aluminium has mainly be used as a wiring material of a semiconductor integrated circuit formed on a semiconductor substrate made of Si. Due to the requirements for higher integration and higher speed of a semiconductor integrated circuit, however, attention is now placed, as the wiring material, on copper excellent in resistance to high stress migration and high electromigration.
The following description will discuss, as a first example of prior art, a method of forming copper wiring on a substrate using a sputtering method with reference to FIGS. 6(a) to (e).
As shown in FIG. 6(a), an insulating layer 101 of SiO2 is deposited on the whole surface of a substrate 100 of Si. Then, as shown in FIG. 6(b), a resist pattern 102 is formed on the insulating layer 101 by photolithography. Then, as shown in FIG. 6(c), the insulating layer 101 is etched with the resist pattern 102 serving as a mask, thereby to form a concave portion 103 for wiring.
As shown in FIG. 6(d), a sputtering method is applied with the use of a target of Si-containing Cu, thereby to deposit a Si-containing copper layer 104 on the whole surface of the insulating layer 101. Then, as shown in FIG. 6(e), that portion of the copper layer 104 which projects from the surface of the insulating layer 101, is removed by a CMP method for example, thereby to form copper wiring 105 formed by the copper layer 104. Then, the substrate 100 is thermally treated, as shown in FIG. 6(f), to form a copper silicide layer 106 on the surface of the copper wiring 105.
The following is the reason of why the copper silicide layer 106 is formed. Copper is liable to be readily oxidized by a heat treatment of about 300xc2x0 C. in the atmosphere of a trace amount of oxygen since copper is low in resistance to oxidation. Accordingly, when the copper wiring 105 comes in contact with an oxygen-containing layer of SiO2 or the like forming the insulating layer 101, the oxidation of copper is advanced with the passage of time in the heating step. Even though the copper wiring 105 does not come in contact with an oxygen-containing layer, the copper wiring 105 comes in contact with the air during the heat treatment. This disadvantageously results in an increase in resistance of the copper wiring 105. Also, the characteristics of the transistor and the like may be degraded by diffusing copper in the copper wiring 105 into the insulating layer 101. In addition, direct deposition of the copper wiring 105 onto the insulating layer 101 results in less adhesiveness between the copper wiring 105 and the insulating layer 101. To prevent the copper wiring 105 from coming in contact with the insulating layer 101 or the air, the copper silicide layer 106 is formed on the surface of the copper wiring 105.
When the wiring rule is small in depositing the copper layer 104 on the insulating layer 101 by a sputtering method, voids 107 are disadvantageously formed as shown in FIG. 6(d). The voids 107 remain also in the copper wiring 105. This disadvantageously contributes to disconnection.
Recently, attention is placed on the technology of forming a copper layer and copper wiring by a CVD (Chemical Vapor Deposition) method using an organic copper complex compound as a precursor. In the field of semiconductor device, study has extensively been made on this technology.
With reference to FIGS. 7(a) to (d) and FIGS. 8(a) to (c), the following description will discuss, as a second example of prior art, a copper wiring forming method by the CVD method.
As shown in FIG. 7(a), an insulating layer 111 of SiO2 is formed on the whole surface of a substrate 110 of Si. Then, as shown in FIG. 7(b), a resist pattern 112 is formed on the insulating layer 111 by photolithography. Then, as shown in FIG. 7(c), the insulating layer 111 is etched with the resist pattern 112 serving as a mask, thereby to form a wiring concave 113.
As shown in FIG. 7(d), a first barrier layer 114 made of WSiN for example is deposited on the wall and bottom surfaces of the wiring concave 113 by a sputtering or CVD method. Then, as shown in FIG. 8(a), a copper layer 115 is deposited on the whole surface of the insulating layer 111 by a CVD method. Then, as shown in FIG. 8(b), that portion of the copper layer 115 which projects from the surface of the insulating layer 111, is eliminated by a CMP method for example, thus forming copper wiring 116 formed by the copper layer 115. Then, as shown in FIG. 8(c), a second barrier layer 117 of WSiN for example is deposited on the whole surfaces of the copper wiring 116 and the insulating layer 111 by a sputtering or CVD method. The first and second barrier layers 114, 117 in the second example of prior art, act in the same way as the copper silicide layer 106 acts in the first example of prior art.
To deposit the copper layer 115 by a CVD method, there is known, as the layer forming material to be supplied to the substrate 110, an organic copper complex compound which is in the form of a liquid or a solid at room temperature. In using a liquid organic copper complex compound in a CVD method, there are known two methods; i.e., a first method in which the organic copper complex compound is caused to pass, in the form of a liquid, through a liquid mass flow meter, the compound is increased in temperature to cause the same to be evaporated by a vaporizer, and the resulting gaseous organic copper complex compound is then introduced into a reaction chamber; and a second method in which a liquid organic copper complex compound is evaporated by bubbling and the resulting gaseous organic copper complex compound is introduced into a reaction chamber through a heated pipe.
As an example of the organic copper complex compound of prior art, there is known, as disclosed by U.S. Pat. No. 5,144,049, L=H2Cxe2x95x90CHxe2x80x94SiMe3 ((hfac)CU(vinyl trimethyl silane)) in which the ligand is the xcex2 diketone type as shown by the following chemical formula: 
When this organic copper complex compound is a solid, the solid organic copper complex compound is dissolved in an organic solvent, e.g., isopropyl alcohol, and the resulting solution is introduced into a reaction chamber in the same manner as done in the liquid organic copper complex compound.
According to the copper wiring forming method using a CVD method, to form a barrier layer on the surface of the copper wiring 116, the first barrier layer 114 and the second barrier layer 117 are required to be formed at different steps. This increases the number of steps to disadvantageously lengthen the whole process.
Further, when copper wiring is formed using an organic copper complex compound of prior art, carbon is put, as impurity, into the copper wiring. This advantageously increases the copper wiring in resistance.
In a copper wiring forming technology using a CVD method, it is a first object of the present invention to reduce the number of the steps of forming barrier layers on the surface of the copper wiring. It is a second object of the present invention to lower the copper wiring in resistance.
A first layer forming material according to the present invention comprises a compound which has a structure of six-membered ring coordinated to Cu and containing Si, and of which general formula is represented by the following chemical formula: 
(wherein X1 and X2 are elements of the VI group of the same or different types which are coordinate-bonded to Cu, at least one of Y1, Y2 and Y3 is Si, L is a group which has a double or triple bond and which is able to supply electrons to Cu, and each of R1 and R2 is an optional element or compound).
According to the first layer forming material, Si is contained in the structure of six-membered ring. Accordingly, when a copper layer formed using the first layer forming material is thermally treated, Si is segregated to the surface of the copper layer to form, on the surface of the copper layer, a barrier layer comprising a copper silicide layer. Thus, when a copper layer is formed by a CVD method using the first layer forming material, a barrier layer can be formed on the surface of the copper layer, without the number of production steps increased.
In the first layer forming material, each of Y1, Y2 and Y3 in the general formula above-mentioned is preferably Si. In this case, since C is not contained in the structure of six-membered ring, a copper layer formed by this layer forming material is lowered in resistance.
In the first layer forming material, L in the general formula above-mentioned is preferably a group of which backbone chain has a double or triple bond and in which all the skeletons contain Si. When a copper layer formed by such a layer forming material, is thermally treated, a barrier layer of a copper silicide layer is sufficiently formed on the surface of the copper layer. This securely prevents the copper layer from being oxidized.
In the first layer forming material, each of R1 and R2 in the general formula above-mentioned is preferably a Si-containing group. When a copper layer formed by such a layer forming material, is thermally treated, a barrier layer of a copper silicide layer is sufficiently formed on the surface of the copper layer. This securely prevents the copper layer from being oxidized.
A second layer forming material according to the present invention comprises a compound which has a structure of six-membered ring coordinated to Cu and containing Si, and of which general formula is represented by the following chemical formula: 
(wherein X1 and X2 are elements of the VI group of the same or different types which are coordinate-bonded to Cu, at least one of Y1, Y2 and Y3 is Si, and each of R1 and R2 is an optional element or compound).
According to the second layer forming material, Si is contained in the structure of six-membered ring. Accordingly, when a copper layer formed using the second layer forming material is thermally treated, Si is segregated to the surface of the copper layer to form, on the surface of the copper layer, a barrier layer formed by a copper silicide layer. Accordingly, when the second layer forming material is used to form a copper layer by a CVD method, a barrier layer can be formed on the surface of the copper layer without the number of production steps increased.
In the second layer forming material, each of Y1, Y2 and Y3 in the general formula above-mentioned is preferably Si. In this case, since C is not contained in the structure of six-membered ring, the copper layer formed by this layer forming material is lowered in resistance.
In the second layer forming material, each of R1 and R2 in the general formula is preferably a Si-containing group. When a copper layer formed by such a layer forming material, is thermally treated, a barrier layer comprising a copper silicide layer is sufficiently formed on the surface of the copper layer. This securely prevents the copper layer from being oxidized.
A first wiring forming method according to the present invention comprises:
a step of using a CVD method to supply, to a substrate, a layer forming material which has a structure of six-membered ring coordinated to Cu and containing Si, and of which general formula is represented by the following chemical formula: 
xe2x80x83(wherein X1 and X2 are elements of the VI group of the same or different types which are coordinate-bonded to Cu, at least one of Y1, Y2 and Y3 is Si, L is a group which has a double or triple bond and which is able to supply electrons to Cu, and each of R1 and R2 is an optional element or compound), thereby to deposit a Si-containing copper layer on the substrate;
a step of forming resist pattern on the copper layer and then etching the copper layer with the resist pattern serving as a mask, thereby to form copper wiring formed by the copper layer; and
a step of thermally treating the substrate, causing Si contained in the copper wiring to be segregated to the surface of the copper wiring, thereby to form a copper silicide layer on the surface of the copper wiring.
According to the first wiring forming method, Si is contained in the structure of six-membered ring of the compound serving as the layer forming material. Accordingly, when copper wiring formed using this layer forming material is thermally treated, Si is segregated to the surface of the copper wiring to form, on the surface of the copper layer, a barrier layer formed by a copper silicide layer.
A second wiring forming method according to the present invention comprises:
a step of using a CVD method to supply, to a substrate, a layer forming material which has a structure of six-membered ring coordinated to Cu and containing Si, and of which general formula is represented by the following chemical formula: 
xe2x80x83(wherein X1 and X2 are elements of the VI group of the same or different types which are coordinate-bonded to Cu, at least one of Y1, Y2 and Yi3 is Si, and each of R1 and R2 is an optional element or compound), thereby to deposit a Si-containing copper layer on the substrate;
a step of forming a resist pattern on the copper layer and then etching the copper layer with the resist pattern serving as a mask, thereby to form copper wiring formed by the copper layer; and
a step of thermally treating the substrate, causing Si contained in the copper wiring to be segregated to the surface of the copper wiring, thereby to form a copper silicide layer on the surface of the copper wiring.
According to the second wiring forming method, Si is contained in the structure of six-membered ring of the compound serving as the layer forming material. Accordingly, when the copper wiring is thermally treated, a barrier layer of a copper silicide layer is formed on the surface of the copper wiring, likewise in the first wiring forming method.
A third wiring forming method of the present invention comprises:
a step of depositing an insulating layer on a substrate;
a step of forming a resist pattern on the insulating layer and then etching the insulating layer with the resist pattern serving as a mask, thereby to form a wiring concave in the insulating layer;
a step of using a CVD method to supply, to the insulating layer, a layer forming material which has a structure of six-membered ring coordinated to Cu and containing Si, and of which general formula is represented by the following chemical formula: 
xe2x80x83(wherein X1 and X2 are elements of the VI group of the same or different types which are coordinate-bonded to Cu, at least one of Y1, Y2 and Y3 is Si, L is a group which has a double or triple bond and which is able to supply electrons to Cu, and each of R1 and R2 is an optional element or compound), thereby to form, in the wiring concave in the insulating layer, copper wiring formed by a Si-containing copper layer; and
a step of thermally treating the substrate, causing Si contained in the copper wiring to be segregated to the surface of the copper wiring, thereby to form a copper silicide layer on the surface of the copper wiring.
According to the third wiring forming method, Si is contained in the structure of six-membered ring of the compound serving as the layer forming material. Accordingly, when the copper wiring is thermally treated, a barrier layer of a copper silicide layer is formed on the surface of the copper wiring, likewise in the first wiring forming method.
A fourth wiring forming method according to the present invention comprises:
a step of depositing an insulating layer on a substrate;
a step of forming a resist pattern on the insulating layer and then etching the insulating layer with the resist pattern serving as a mask, thereby to form a wiring concave in the insulating layer;
a step of using a CVD method to supply, to the insulating layer, a layer forming material which has a structure of six-membered ring coordinated to Cu and containing Si, and of which general formula is represented by the following chemical formula: 
xe2x80x83(wherein X1 and X2 are elements of the VI group of the same or different types which are coordinate-bonded to Cu, at least one of Y1, Y2 and Y3 is Si, and each of R1 and R2 is an optional element or compound), thereby to form, in the wiring concave in the insulating layer, copper wiring formed by a Si-containing copper layer; and
a step of thermally treating the substrate, causing Si contained in the copper wiring to be segregated to the surface of the copper wiring, thereby to form a copper silicide layer on the surface of the copper wiring.
According to the fourth wiring forming method, Si is contained in the structure of six-membered ring of the compound serving as the layer forming material. Accordingly, when the copper wiring is thermally treated, a barrier layer formed by the copper silicide layer is formed on the surface of the copper wiring, likewise in the first wiring forming method.
Thus, according to each of the first to fourth wiring forming methods above-mentioned, Si is contained in the structure of six-membered ring of the layer forming material. Accordingly, when the copper wiring is thermally treated, Si is segregated to the surface of the copper wiring to form, on the surface of the copper wiring, a barrier layer formed by a copper silicide layer. Thus, a barrier layer can be formed on the copper wiring without the number of production steps increased, although the copper wiring is formed by a CVD method.